I'm looking for an anime that shows a character standing/hovering over someone (preferably of the opposite sex) while they sleep. And then later on, having captured that person and threatening them with small weapons of sorts (knives, swords, etc).

The creepier the better, and the more animated they get when they are threatening would be a bonus.

I realize I have painted a pretty specific thing, hopefully its not asking too much.

She is the classic yandere. In the series, she is the main (male) character's psychotically obsessed stalker/girlfriend/main ally. Obsessed enough to kill anyone who gets near him, kidnap him, and do this:

There's also lots of scenes of her doing this sort of thing to other characters that you can exploit:

The Birds are using humanity in order to throw something terrifying at this green pig. And then what happens to us all later, that’s simply not important to them…